1). Field of the Invention
This invention relates to a method of and a system for sealing an epitaxial silicon layer formed on a semiconductor wafer.
2). Discussion of Related Art
Integrated circuits are formed in and on silicon and other semiconductor wafers. Wafers are made by extruding an ingot from a silicon bath and sawing the ingot into multiple wafers. In the case of silicon, the material of the wafers is monocrystalline. An epitaxial silicon layer is then formed on the monocrystalline material of the wafer. The epitaxial silicon layer is typically doped with boron and has a dopant concentration of about 1xc3x971016 atoms per centimeter cube. A typical epitaxial silicon layer is about five microns thick. The material of the epitaxial silicon layer has better controlled properties than the monocrystalline silicon for purposes of forming semiconductor devices therein and thereon.
Once the epitaxial silicon layer is formed, the wafer is removed from the wafer processing chamber and exposed to ambient air. The air oxidizes the exposed epitaxial silicon layer to form a native oxide layer thereon. The epitaxial silicon layer and the native oxide layer are exposed to contaminants in the air and are usually filled with impurities and particles. When semiconductor devices are formed on a surface which is filled with impurities, the electronic devices often fail.
It has been suggested that exposure of an epitaxial silicon layer to ozone gas will provide an efficient process for forming a very pure oxide layer on the epitaxial silicon layer. Furthermore, U.S. Pat. application Ser. No. 09/350,805 describes a system which is used to process a wafer so that an epitaxial silicon layer is formed thereon, followed by exposure to ozone gas in a loadlock chamber. The wafer is however exposed with other wafers and exposure takes at least 20 minutes. Such slow exposure may inhibit a process where only a few wafers are processed.
A system for processing a wafer is provided comprising a chamber body, a window, a wafer holder, an ozone generation chamber, and at least one ultraviolet lamp. The window is transmissive to ultraviolet light and is mounted to the chamber body. The chamber body and the window jointly form a chamber. The chamber defines an enclosure and has at least a first opening for transferring a wafer therethrough from an area externally of the chamber into the enclosure. The wafer holder is located within the chamber to hold the wafer in the enclosure. The ozone generation chamber is located externally of the chamber and is in communication with the enclosure. The ultraviolet lamp has a filament which, when electric current flows therethrough creates ultraviolet light. The ultraviolet light therefrom radiates through a first amount of unconverted gas in the ozone generation chamber so that the first amount of unconverted gas is converted to a first amount of ozone gas. The first amount of ozone gas flows from the ozone generation chamber into the enclosure and the wafer held by the wafer holder is exposed to the first amount of ozone gas. The ultraviolet light also radiates through the window and then through a second amount of unconverted gas in the enclosure so that the second amount of unconverted gas is converted to a second amount of ozone gas. The wafer held by the wafer holder is also exposed to the second amount of ozone gas.